A tertiary data storage system is a data storage system that stores data in a medium that is not directly under the control of a processing unit, but is accessible via mechanical means of mounting the medium to an input/output device (“I/O drive”) of the processing unit. Tertiary storage or tertiary memory provides a third level of storage (e.g., aside from primary storage that is directly accessible to the processing unit and secondary storage that is indirectly accessible to the processing unit through a staging area). Typically, tertiary data storage involves a robotic mechanism which can insert or remove mass storage media into or from an I/O drive according to a storage system's demands. Traditionally, tertiary data storage is used for archiving rarely accessed information since it is much slower than secondary storage (e.g., 5-60 seconds vs. 1-10 milliseconds). This is primarily useful for extraordinarily large data stores that are accessed without human operators. Examples include tape libraries and optical jukeboxes.
In a conventional tertiary data storage architecture, when a computer needs to read information from the tertiary storage, it can consult a catalog database to determine which data storage medium (e.g., tape or disc) contains the information. Next, the computer can instruct a robotic arm to fetch the medium and place it in an I/O drive. When the computer has finished reading the information, the robotic arm can return the medium to its assigned place in a “library” of the tertiary storage.
Tertiary storage can be considered a form of cold storage. The medium is recorded, and then physically removed or disconnected. For example, the medium can be an optical disc (e.g., Blu-Ray™ disc, a compact disc (CD), a digital versatile disc (DVD), Archival Disc™ (AD), or any combination thereof). Tertiary storage can be used as a last resort data backup. In case of a disaster, for example a fire, destroys the original data, a medium in a remote location is probably unaffected, enabling disaster recovery. The off-line nature of the data storage medium increases general information security, since it is physically inaccessible from a computer when not connected to the I/O drive, and data confidentiality or integrity cannot be affected by computer-based attack techniques. Also, if the information stored for archival purposes is rarely accessed, off-line storage is less expensive than other forms of data storage. Nevertheless, the long delays associated with using tertiary data storage remains a challenge, and discourages people from implementing them for mass data applications.
The figures depict various embodiments of this disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of embodiments described herein.